The present invention relates to a vibration actuator, and more particularly to a vibration element which moves in relation to and is in compressive contact with a relative moving member.
As prior art technology, for example, a longitudinal-bending type of vibration actuator is known in which a drive force is obtained by causing longitudinal vibrations and bending vibrations to arise harmonically in an elastic member.
FIG. 12 (PRIOR ART) is a front view of a prior art longitudinal-bending vibration actuator. As illustrated in FIG. 12, vibration element 10 includes an elastic member 11 which is designed in a rectangular flat plate form. Elastic member 11 is designed to have a resonance frequency value which is very close to a resonant frequency of a first order longitudinal vibration and a fourth order bending vibration (or eighth order bending vibration). As illustrated, two electro-mechanical conversion elements 12a, 12b (piezoelectric elements) are affixed to the same side surface of elastic member 11.
Two alternating voltages which differ in phase and have respective frequencies close to the above resonant frequencies are impressed on the piezoelectric elements 12a, 12b in vibration element 10. Accordingly, two harmonized vibrations are generated in elastic member 11.
Driving force output members 11a, 11b are formed in a projecting shape from portions of elastic member 11 and become anti-nodes of the fourth order bending vibration. The fourth order bending vibration arises in the flat, opposite, side surface of elastic member 11. The tips of driving force output members 11a, 11b are periodically displaced in elliptic form. Accordingly, the compressive contact of the tips of driving force output members 11a, 11b output a driving force to relative moving member 40.
If relative moving member 40 is fixed, vibration element 10 propels itself in a trajectory in a right-hand direction or a left-hand direction in relation to relative moving member 40. Moreover, in the case that vibration element 10 is fixed, relative moving member 40 becomes a driven object and accordingly is driven right or left with respect to vibration element 10.
In order for the sliding resistance between the contact surface of relative moving member 40 and driving force output members 11a, 11b to be low, a sliding material (not shown in the drawing) is affixed to relative moving member 40 by way of adhesive or the like. Moreover, a mirror surface lapping process is generally performed on the sliding surfaces of driving force output members 11a, 11b and relative moving member 40 in order, similarly, to reduce the sliding resistance.
However, in the prior art vibration actuators, "wear particles" appears after the vibration actuators are driven for a long period of time. These wear particles result from sliding, and adheres to the contact surfaces of elastic member 11 and relative moving member 40. The adhesion of the wear particles has the effect of reducing the drive force. Accordingly, a stabilized drive may only be performed for a relatively short period time.
Moreover, during reciprocating motion of vibration element 10, wear particles become marked at the reversal positions and the positions nearly adjacent to the reversal positions along the sliding surface of relative moving member 40. Thus, another problem is that movement of vibration element 10 may become reduced at either of the reversal positions. In the case of a fixed vibration element, relative moving member 40 similarly performs a reciprocating motion, and wear particles are markedly deposited at the reversal positions along relative moving member 40. In a worst case scenario, relative moving member 40 is stopped at one of the reversal positions.
Furthermore, when a mirror surface is used for relative moving member 40 and a lapping process (polishing process) is carried out on the sliding surface of relative moving member 40, there is a problem that wear particles tend to enter very fine scratches in the mirror lapped surface and adheres therein.